Ambyopia is found in several varieties and in a significant fraction of the population. It involves a sensory deficit manifested by lowered acuity except in the dark, lowered foveal contrast sensitivity and flicker fusion, lowered increment sensitivity and abnormal contour interaction. Most of these manifestations of deficit have been shown to be attributable to loci at or distal to the visual cortex. Theories to explain the deficit(s) range from receptoral malorientation, abnormal lateral inhibition and cortical inhibition to attentional and ocular motility abnormalities. However previous research has assumed constant some properties of the visual system that might themselves explain all or part of the observed difficiency. The objective of this research is to psychophysically measure the dark light, quantum efficiency, criterion variability, stimulus uncertainty and neural interactions in the amblyopic eye and to compare them with measurements of normal eyes. For this purpose a number of new experimental techniques have been developed. It is planned to study first the oblique effect (a naturally occuring "amblyopia in normal eyes) next meridional amblyopia (an amblyopia associated with linear stimuli or stimuls combinations of particular orientation seemingly due to uncorrected astigmatism) and finally anisometropic and strabismic amblyopia. The experiments developed for use in this research stem from analogous physiological experiments and are unique in their ability to examine the physiologic quantities mentioned above. They should prove useful in the analysis of other sensory deficits.